Breath test system

ABSTRACT

The invention relates to a breath test system that is unobtrusive in that it does not require a person subjected to the system to take any other action to breath. It comprises a sensor unit ( 5 ) configured to sense the presence or concentration of a volatile substance, present in air flowing through a predefined inlet area ( 4 ), and to generate a signal corresponding to the concentration of said substance. There is also provided an apparatus ( 2, 3 ) configured to detect the presence of a person at a position in the vicinity of said input area, and having means for registering said presence, and further configured to respond to said presence by delivering an output. This said apparatus includes a unit configured to call for immediate attention of said person, upon said registration of the presence of said person, and a unit configured to provide instructions to said person to direct an expiratory air flow towards said inlet area ( 4 ). An analyzer ( 10 ) for the determination of breath substance concentration of said person is also provided, the determination being based on said signal corresponding to the substance concentration.

This invention is concerned with a system for the unsupervised sensingthe presence/concentration of substances, such as ethyl alcohol, withinthe expired breath of a person.

BACKGROUND OF THE INVENTION

Breath Alcohol Concentration (BrAC) is related to Blood AlcoholConcentration (BAC) by the approximate relationBrAC[mg/l]=0.5*BAC[mg/g]. Other substances will have differentcoefficients.

Supervised breath tests according to the state of the art are beingperformed by the police in order to prevent drunk driving. For the samepurpose, unsupervised tests using alcolocks in vehicles are also beingincreasingly used. Sensor technologies include catalytic semiconductors,fuel cells and infrared spectroscopy. Performance with respect toaccuracy, specificity, environmental immunity, and response time, ishighly variable between different devices available on the market.Devices for breath test include sensor elements providing a signalrepresenting BrAC after taking a deep breath, and emptying the airwaysvia a tight-fitting mouthpiece, which for hygienic reasons has to be aseparate, disposable item. In order to ensure a correct determination,the test person is required to deliver a forced expiration at almostfull vital capacity. This requires a substantial effort, especially forpersons with limited respiratory capacity. The handling of mouthpiecesis costly, time-consuming and represents an undesired source of errordue to water condensation.

The basic techniques of breath analysis were developed during the secondhalf of the 20^(th) century. More recently, a movement towards lessobtrusive means for breath test has been noted. Olsson et al (WO98/20346) disclosed a system solution in which accurate measurementscould be performed without a mouthpiece using water vapor as a tracergas. Lopez (U.S. Pat. No. 5,458,853) reported another approach, usingultrasound to correct for the dependence on distance between the deviceand the user's mouth. Hök et al (GB 2431470) disclosed a system solutionusing carbon dioxide (CO₂) as a tracer gas, combined with a simplealgorithm for correction of a diluted breath sample. Still anotherapproach was reported by Lambert et al (SAE World Congress Apr. 3-6,2006). The air within a vehicle cabin was monitored, and an alcoholadsorbing material was used to accumulate the sample to enhanceresolution. Again, CO₂ was used as a tracer gas.

SUMMARY OF THE INVENTION

A specific object of the present invention is to reduce the effortrequired by the person to be tested to a minimum, without compromisingreliability. Other objects are to reduce the total time required for abreath test, and that the system is self-instructive even for aninexperienced person.

The present invention is based on a few critical elements which incombination will provide the necessary characteristics. First, there isprovided a sensor unit providing a signal corresponding to theinstantaneous alcohol concentration of air flowing through a predefinedinlet area. A predefined inlet area is one or several openings, allowingair to be continuously flowing from the inlet area to the sensor.Second, there is provided an apparatus responsive of the presence of aperson at a position in the vicinity of the sensor inlet area, and alsoincluding a unit for calling for and directing the immediate attentionof the person, and of providing instruction to direct expiratory airflow towards the inlet area. This directed breath is a deliberate act bythe person. Third, an analyzer is included for the determination ofbreath alcohol concentration of said person based on the sensor signal.

The combined function of the basic elements is necessary and sufficientfor breath tests of experienced users to be effortlessly performedwithin 2-3 seconds at full privacy, without a mouthpiece, and withoutinterfering with normal activities, such as on-going conversation. Theinexperienced user is guided by automatically communicated instructionsto successful completion of the test.

The present invention allows breath tests to be performed in a varietyof circumstances which have hitherto been inaccessible. The improveduser friendliness combined with the possibility of vehicle integrationmay be an important step towards preventing drunk driving on a muchlarger scale than with products available at the present. This isbelieved necessary to reduce the high mortality of alcohol relatedtraffic accidents. Other promising application areas are sobrietycontrol of staff with critical tasks, and of audience arriving at anarena. It may also be used in various self test scenarios, e.g. in thetreatment of alcoholics. The possibility of unobtrusive breath tests isexpected to become important for diagnostic purposes in emergencymedicine. For this purpose, a large number of volatile substances are ofinterest in addition to ethyl alcohol.

In view of the shortcomings of prior art systems, the inventors havedevised a novel system.

Thus, claim 1 defines a breath test system, including a sensor unit (5)configured to sense the presence or concentration of a volatilesubstance, present in air flowing through a predefined inlet area (4),and to generate a signal corresponding to the concentration of saidsubstance; an apparatus (2, 3) configured to detect the presence of aperson at a position in the vicinity of said input area, and havingmeans for registering said presence, and further configured to respondto said presence by delivering an output, said apparatus including aunit configured to call for immediate attention of said person, uponsaid registration of the presence of said person; and a unit configuredto provide instructions to said person to direct an expiratory air flowtowards said inlet area (4); an analyzer (10) for the determination ofbreath substance concentration of said person, the determination beingbased on said signal corresponding to the substance concentration.

The main advantage of the system is that it is unobtrusive, i.e. it doesnot unduly interfere with the person subjected to the use of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described below with reference to the drawingsin which

FIG. 1 shows a schematic drawing of the system according to oneembodiment.

FIG. 2 shows a flow graph of the system function.

FIG. 3 a shows a time sequence of typical breath tests performed withthe system according to the invention for an experienced person, and

FIG. 3 b shows a time sequence of typical breath tests performed withthe system according to the invention for an inexperienced person.

DETAILED DESCRIPTION

The present invention involves both physical attributes and functionalcharacteristics, as evident both in the enclosed claims and the detaileddescription.

FIG. 1 is a schematic drawing (not to scale) of one embodiment of thesystem 1 according to the invention. The system 1 may be built into aseparate physical enclosure, or being part of inventories, e.g. in avehicle cabin. A test person 12 is shown positioned in the vicinity ofan inlet area 4 of the sensor unit 5, equipped with a sensor element 8generating a signal corresponding to the ethyl alcohol concentration ofthe air flowing through the inlet area 4. Means for active transport ofair through the sensor unit 5 is provided by a fan or pump 9, preferablyincluding means for controlling the volume flow. The inlet area 4constitutes one or several openings, into which air can be freelyflowing, or driven by the fan 9. Preferably, a particle filter 11 e.g.made from porous material is included in the inlet area 4. This preventsparticles and aerosols from contaminating the sensor unit 5 while notimpeding the air flow to any significant degree. When the person 12 isdirecting expiratory air towards the inlet area 4 from a distance notexceeding 50 cm, the air flowing through the sensor unit 5 will consistof a mixture of ambient and expiratory air from the person 12.

As already explained in the background, a central characteristic of thepresent system is to obtain cooperation with the person 11 during ashort moment of time. The apparatus configured for achieving thisincludes means for registration 2 of the presence of a person 12 at aposition in the vicinity of the inlet area 4, and an audiovisual unit 3.The implementation of the means of registration 2 is highly depending onthe actual application and could include a microswitch indicating dooropening/closure, microphone, camera, contactless detector usingultrasound or infrared radiation, force sensor responding to the weightof the person. It may include means for identification of the person byvoice control, image analysis, barcode reading, or biometric analysis.The audiovisual unit 3 preferably includes a loudspeaker 3 a and adisplay 3 b. The loudspeaker 3 a may generate artificial speech orsymbolic sound tracks, and the display 3 b may convey text, images,icons or other symbols.

Preferably, the audiovisual unit 3 is located in close vicinity to theinlet area 4 of the sensor unit 5, in order to direct the person's 12attention to this area. It is capable of calling for the immediateattention of the person 12 upon presence registration or at some laterinstant. It is also capable of conveying an instruction, even a detailedone, in the case that the person 12 may need one.

The location of the audiovisual unit 3 in close vicinity to the inletarea 4 is particularly important in the case of an experienced butdistracted or otherwise un-attentive person 12. When reminded by thesignals from the audiovisual unit 3, the experienced person 12 willreact with minimal time delay, and deliver a directed breath towards theinlet area 3. Alternative solutions would increase the mental load ofthe person 12.

From research in experimental psychology it is known that the reactiontime of a person may vary from 0.2 to several seconds depending on thedegree of distraction, mental load, and choice options. The capabilityof the present invention to both call for and direct the attention ofthe experienced person 12 to the sensor inlet area is thus highlyimportant in order to save time.

As a consequence of mixing between ambient and expiratory air, thesignal generated by the sensor element 8 will be diminished by a factorcorresponding to the dilution of the expiratory air. Therefore, anothersensor element 7 is included in addition to the element 8, for measuringthe concentration of a tracer gas, e.g. carbon dioxide (CO₂) or watervapor. Since the tracer gas concentration is approximately constant whenleaving the airways on expiration, it is possible to obtain a fairapproximation of the degree of dilution of the air entering the sensorunit 5. Another option for a tracer signal besides CO₂ and H₂O istemperature. The temperature of expiratory air is almost the same asbody temperature as it leaves the mouth or nose but is cooled will getcloser to ambient upon mixing.

The sensor elements 7 and 8 constitute the receiver ends of ameasurement cell for infrared (IR) transmission measurement. From aninfrared emitter 6, preferably a blackbody radiating element, a beam ofbroadband infrared radiation is illuminating the cell, and eventuallyafter multiple reflections it will reach the elements 7, and 8.Preferably, the emitter 6 is modulated at a frequency, e.g. 5 Hz, abovethe frequency band of typical signals. Each of the sensor elements 7 and8 include thermopile detectors of infrared radiation with bandpassinterference filters tuned to the absorption peak of the substance to bedetected. The element 8 includes a filter with the pass band within theinterval 9.1 . . . 9.9 μm for ethyl alcohol, and the element 7 thefilter in the interval 4.2 . . . 4.3 μm in the case of CO₂ as tracergas. Water vapor, an alternative tracer gas, has strong absorption inthe wavelength intervals 2.5 . . . 2.8 μm and 5.7 . . . 6.9 μm. Othercombinations of gases and filter characteristics are possible. Acetone,acetaldehyde, methyl alcohol, carbon monoxide, methane, ethane, propane,pentane, hexane, heptane, octane, isoprene, ammonia, hydrogen sulfide,methyl mercaptan, ethyl acetate, dimethyl ether, diethyl ether, benzene,toluene, methyl ethyl ketone, and methyl isobutyl ketone are examples ofvolatile substances that may be of interest interest from a diagnosticor toxicological perspective.

The optical path from the IR emitter 6 to the detectors 7, and 8 maydepend on the concentration range and the absorption coefficients of theactual substances. CO₂ has strong absorption and high concentration inexpiratory air which calls for a short optical path, 10-25 mm. Foralcohol detection below the legal concentration limits, path lengths ofmore than 0.5 m may be necessary. By folding the optical path usingmultiple reflections, the length/width/height of the sensor unit 5 canstill be kept smaller than 70/30/15 mm.

The sensor unit 5 responds almost instantaneously, i.e. within afraction of a second, to concentration variations occurring at the inletarea 4. This is partly due to the small distance between the inlet area4 and the sensor unit 5, typically 10-20 mm, its small inner volume,typically 20-60 ml, and the air volume flow, typically 100-200 ml/sec,generated by the fan 9. It is also due to the relatively fast modulationfrequency of the infrared emitter. The signal information extracted fromthe sensor elements 7 and 8 is represented as the amplitude of themodulation frequency.

The signals from the sensor elements 7, 8 are brought to an analyzer 10,which preferably includes a general purpose digital microcontroller withcapacity to execute signal algorithms, and also controlling theaudiovisual unit 3, IR emitter 6, fan or pump 9. Signal conversionbetween different formats, including analog signals, can be managed bythe microcontroller 10, which will also be capable of communicating withexternal units, e.g. an actuator unit for taking action or counteractiondepending on the result of the breath test. Electric power for thesystem 1 can either be obtained from a battery or from an external powersource. The system 1 can be designed as a stand-alone unit, or as anintegrated part of other inventories, e.g. a vehicle compartment orentrance of building or workplace. Preferably, the inlet area 4 includesmeans for protection of the sensor unit 5, e.g. a lid which is closedwhen the system 1 is inactive.

In order to meet requirements on electromagnetic emission and immunity,the system according to the invention includes capacitive and inductiveelectronic elements for protective purposes. In addition, the elements 7and 8 and their associated analog input stages are preferably equippedwith differential preamplifiers in order to suppress the influence ofcommon mode interference.

The system according to the invention is preferably confined in a box tobe wall-mounted in such a way that the means for registration 2,audiovisual unit 3, and inlet area 4, are located on one side of the boxand thereby accessible through a hole in the wall.

FIG. 2 shows a flow diagram of the system function according to theinvention. The system is started or initiated either manually orautomatically, by some external control signal. In the case of avehicle, the start signal could be unlocking of the vehicle doors. Theinitiating phase preferably involves some self-testing functions of thesystem, to make sure that no functional errors have occurred since theprevious test occasion. The initiating phase could also includepreheating of sensitive components and stabilization of signals.

When the system is ready for test it will remain in a standby conditionuntil the presence of a person within the predefined position isdetected. As previously described, detection may or may not involveidentification of the person, and could require two-way communicationbetween the person and the system. After or during the presencedetection step, the system will call for the person's attention bycoordinated flashing light, distinctive and directional sound combinedwith specific symbol or icon representing the breath test.

An experienced person is then expected to direct expiratory air towardsthe sensor inlet area, whereas an inexperienced person may require amore or less detailed instruction on how to proceed. Example ofinstruction provided verbally or as a text message: “Take a deep breath,lean over, open your mouth wide and exhale gently.” Alternatively,instructions are provided by text, still or moving images, graphicsymbols or other means. If the criteria for breath detection are notfulfilled after one round of instruction, repeated instructions may bedelivered at increasing level of detail.

The criteria for breath detection preferably involve tracer gasdetection as previously described. In the case of CO₂ as tracer gas, asimple criterion is reaching a threshold CO₂ concentration of e.g. 2500ppm (parts per million), which corresponds to a dilution factor of 20(alveolar CO₂ concentration being approximately 5 vol %, or 50 000 ppm).Additional criteria could be related to the time derivative of the CO₂signal. The simultaneously measured alcohol concentration will in thiscase have to be multiplied with 20 in order to obtain an estimatedbreath alcohol concentration. The criteria for breath detection shouldalso include correction for background CO₂ concentration, which istypically 400-600 ppm in normal environments. A mathematical expressionor algorithm will normally be adequate for defining the criteria, usingsettable parameters to adapt for variations between differentconditions. Such an algorithm can be implemented for execution in realtime using standard microcontrollers.

The level of dilution is a measure of the signal quality. Highconcentration (small dilution factor) provides high confidence of thedetermination, whereas the influence of interfering factors, such asother nearby persons, will increase with degree of dilution. Preferably,the result of the breath test is presented not only as a concentrationbut also in terms of an estimated error depending on the dilutionfactor.

Breath detection may in some applications override the presencedetection as symbolized in FIG. 2 by the dotted line short-cutting boththe ‘attention’ and ‘instruction’ sequences. Another way of expressionis to include the tracer gas detection into the ‘means of registration’.

Determination of BrAC is performed by another algorithm based on thecorrelation between the signals from the sensor elements 7 and 8. Whenthe sensor unit 5 is receiving expired air from a person, both sensorelements exhibit concentration peaks which occur almost simultaneously.An average BrAC value is obtained by multiplying a number of measuredalcohol concentrations by their respective dilution factors. Byaveraging, the effect of noise and interference is reduced. A small timedifference between the CO₂ and the alcohol signals due to differencescaused by the anatomic dead space or by the design of the sensor unit 5is also possible to accommodate in the algorithm.

The completion and result of a breath test defined by fulfillment of thecriteria for breath detection, is preferably communicated to the person,e.g. using the audiovisual unit 3.

In the flow diagram of FIG. 2 , the further steps taken aftertermination of the actual breath test are not included, since they maybe highly depending on the actual application of the breath test. Suchsteps may involve rule-based decision for controlling action orcounteraction based on the determination, e.g. enable/disable functionsof a vehicle or locking/unlocking of door.

FIG. 3 shows time sequences of typical breath tests performed with thesystem according to the invention for (a) and experienced person, and(b) an inexperienced person. From top to bottom the signals representedare: ‘P’ presence, ‘C’ communication, ‘T’ tracer gas, ‘A’ alcohol inboth diagrams 3 (a) and 3 (b).

In the time sequence of FIG. 3 (a) a person is detected within the firsthalf second, and is almost immediately followed by the ‘attention’communication to the experienced test person, who responds after anotherhalf a second by distinctive peaks representing both the tracersubstance and alcohol. After two seconds, the breath test is completed.

The time sequence of FIG. 3 (b) follows a somewhat different pattern.The inexperienced test person does not immediately respond, but requiresa short instruction before supplying an approved breath. The entiresequence is completed after 15 seconds.

1.-15. (canceled)
 16. A breath test system for determining theconcentration of a volatile substance present in a breath of air, saidbreath test system comprising: a chamber having an inlet for receiving abreath of air, an outlet, and a lumen extending between said inlet andsaid outlet; an electromagnetic emitter configured to emit light intosaid lumen of said chamber; at least one electromagnetic detectorconfigured to detect light emitted by said electromagnetic emitter aftersaid light has passed through said lumen, said at least oneelectromagnetic detector being configured to generate a signalcorresponding to at least one characteristic of said light after saidlight has passed through said lumen and been received by said at leastone electromagnetic detector; said light emitted by said electromagneticemitter and detected by said at least one electromagnetic detector beingdirected along an optical path contained within said chamber; ananalyzer for analyzing the signal generated by said at least oneelectromagnetic detector so as to determine (i) whether a breath of airhas entered said lumen of said chamber; and (ii) if a breath of air hasentered said lumen of said chamber, the concentration of the volatilesubstance present in a breath of air.
 17. The breath test systemaccording to claim 16, wherein said breath test system comprises a firstelectromagnetic detector providing a first signal corresponding to theconcentration of the volatile substance within the breath of air and asecond electromagnetic detector providing a second signal correspondingto the concentration of a tracer substance within the breath of air,said determination of the concentration of the volatile substancepresent in the breath of air taking said tracer substance concentrationinto account.
 18. The breath test system according to claim 16, whereinsaid volatile substance is acetone, acetaldehyde, methanol, ethanol,carbon monoxide, methane, ethane, propane, pentane, hexane, heptane,octane, isoprene, ammonia, hydrogen sulfide, methyl mercaptan, ethylacetate, dimethyl ether, diethyl ether, benzene, toluene, methyl ethylketone, or methyl isobutyl ketone or a combination thereof.
 19. Thebreath test system according to claim 16, wherein a response time ofsaid breath test system is shorter than one second.
 20. The breath testsystem according to claim 16, wherein said system comprises registrationmeans for registering the presence of a person in the vicinity of saidinlet, wherein the registration means comprises a microphone, and meansfor identification of the person using voice recognition, and furtherwherein said system further comprises a camera or other opticaldetector, and means for identification of the person using imageanalysis, bar code reading or biometrics.
 21. The breath test systemaccording to claim 17, wherein said first electromagnetic detector andsaid second electromagnetic detector are based on substance-specificinfrared absorption in predetermined wavelength bands, and furtherwherein said predetermined wavelength band for said firstelectromagnetic detector is 9.1-9.9 μm corresponding to ethyl alcohol,and said predetermined wavelength band for said second electromagneticdetector is 4.2-4.3 μm corresponding to CO₂.
 22. The breath test systemaccording to claim 16, comprising means for active transport of air fromsaid inlet to said at least one electromagnetic detector and saidoutlet.
 23. The breath test system according to claim 16, whereinattention of a person is called for by coordinated flashing of a light,and a distinctive sound combined with a specific symbol or iconrepresenting said breath test.
 24. The breath test system according toclaim 16, wherein said system is configured to provide instructions to aperson in the vicinity of said inlet to direct a breath of air into saidinlet such that the breath of air enters said lumen of said chamber,wherein said instructions are provided to the person verbally or as textmessage, step by step and with the level of detail provided to theperson increasing with time.
 25. The breath test system according toclaim 16, wherein said breath test system further comprises a displayfor communicating messages of text, symbols, icons or images, or aloudspeaker for communicating recorded spoken messages, or symbolicsound tracks.
 26. The breath test system according to claim 16, whereinsaid determination of the concentration of the volatile substancepresent in the breath of air accounts for quality criteria, wherein saidquality criteria includes at least one of a concentration of tracer gasexceeding a predefined threshold and background variations of saidsignal being below a predefined upper limit.
 27. The breath test systemaccording to claim 16, wherein said system is integrated into theinterior of the vehicle compartment or an entrance of building or aworkplace.
 28. The breath test system according to claim 16, wherein thetotal test time of said breath test system does not exceed five seconds.29. The breath test system according to claim 16, further comprisingcapacitive and inductive electronic elements for protective purposes,and wherein said at least one electromagnetic detector and associatedanalog input stages is equipped with differential preamplifiers in orderto suppress the influence of common mode interference.
 30. The breathtest system according to claim 16, wherein said breath test system isconfined in a box adapted to be wall-mounted in such a way that meansfor registering a presence of a person and said inlet are located on oneside of the box and thereby accessible through a hole in the wall towhich said breath test system is mounted.
 31. A method for determiningthe concentration of a volatile substance present in a breath of air,said method comprising: providing a breath test system comprising: achamber having an inlet for receiving a breath of air, an outlet, and alumen extending between said inlet and said outlet; an electromagneticemitter configured to emit light into said lumen of said chamber; atleast one electromagnetic detector configured to detect light emitted bysaid electromagnetic emitter after said light has passed through saidlumen, said at least one electromagnetic detector being configured togenerate a signal corresponding to at least one characteristic of saidlight after said light has passed through said lumen and been receivedby said at least one electromagnetic detector; said light emitted bysaid electromagnetic emitter and detected by said at least oneelectromagnetic detector being directed along an optical path containedwithin said chamber; an analyzer for analyzing the signal generated bysaid at least one electromagnetic detector so as to determine (i)whether a breath of air has entered said lumen of said chamber; and (ii)if a breath of air has entered said lumen of said chamber, theconcentration of the volatile substance present in a breath of air;passing a breath of air into said lumen of said chamber; using saidelectromagnetic emitter to emit light into said lumen of said chambersuch that said light passes through said breath of air in said lumen ofsaid chamber, such that said light is detected by said at least oneelectromagnetic detector so as to generate said signal; analyzing saidsignal so as to determine (i) whether a breath of air has entered saidlumen of said chamber; and (ii) if a breath of air has entered saidlumen of said chamber, the concentration of the volatile substancepresent in a breath of air.
 32. The method according to claim 31,wherein said breath test system comprises a first electromagneticdetector providing a first signal corresponding to the concentration ofthe volatile substance within the breath of air and a secondelectromagnetic detector providing a second signal corresponding to theconcentration of a tracer substance within the breath of air, saiddetermination of the concentration of the volatile substance present inthe breath of air taking said tracer substance concentration intoaccount.
 33. The method according to claim 31, wherein said volatilesubstance is acetone, acetaldehyde, methanol, ethanol, carbon monoxide,methane, ethane, propane, pentane, hexane, heptane, octane, isoprene,ammonia, hydrogen sulfide, methyl mercaptan, ethyl acetate, dimethylether, diethyl ether, benzene, toluene, methyl ethyl ketone, or methylisobutyl ketone or a combination thereof.
 34. The method according toclaim 31, wherein a response time of said breath test system is shorterthan one second.
 35. The method according to claim 31, wherein saidsystem comprises registration means for registering the presence of aperson in the vicinity of said inlet, wherein said registration meanscomprises a microphone, and means for identification of the person usingvoice recognition, and further wherein said system further comprises acamera or other optical detector, and means for identification of theperson using image analysis, bar code reading or biometrics.
 36. Themethod according to claim 32, wherein said first electromagneticdetector and said second electromagnetic detector are based onsubstance-specific infrared absorption in predetermined wavelengthbands, and further wherein said predetermined wavelength band for saidfirst electromagnetic detector is 9.1-9.9 μm corresponding to ethylalcohol, and said predetermined wavelength band for said secondelectromagnetic detector is 4.2-4.3 μm corresponding to CO₂.
 37. Themethod according to claim 31, comprising means for active transport ofair from said inlet to said at least one electromagnetic detector andsaid outlet.
 38. The method according to claim 31, further comprisingcalling attention to a person, wherein the attention of the person iscalled for by coordinated flashing of a light, and a distinctive soundcombined with a specific symbol or icon representing said breath test.39. The method according to claim 31, wherein said method furthercomprises providing instructions to a person in the vicinity of saidinlet to direct a breath of air into said inlet such that the breath ofair enters said lumen of said chamber, wherein said instructions areprovided to the person verbally or as text message, step by step andwith the level of detail provided to the person increasing with time.40. The method according to claim 31, wherein said breath test systemfurther comprises a display for communicating messages of text, symbols,icons or images, or a loudspeaker for communicating recorded spokenmessages, or symbolic sound tracks.
 41. The method according to claim31, wherein said determination of the concentration of the volatilesubstance present in the breath of air accounts for quality criteria,wherein said quality criteria includes at least one of a concentrationof tracer gas exceeding a predefined threshold and background variationsof said signal being below a predefined upper limit.
 42. The methodaccording to claim 31, wherein said system is integrated into theinterior of the vehicle compartment or an entrance of building or aworkplace.
 43. The method according to claim 31, wherein the total testtime of said breath test system does not exceed five seconds.
 44. Themethod according to claim 31, further comprising capacitive andinductive electronic elements for protective purposes, and wherein saidat least one electromagnetic detector and associated analog input stagesis equipped with differential preamplifiers in order to suppress theinfluence of common mode interference.
 45. The method according to claim31, wherein said breath test system is confined in a box adapted to bewall-mounted in such a way that means for registering a presence of aperson and said inlet are located on one side of the box and therebyaccessible through a hole in the wall to which said breath test systemis mounted.